The present invention relates to a multi-core core optical waveguide, and more particularly to multi-core waveguide having a cladding disposed about at least a pair of inner cores and having an outer transverse dimension of at least 0.3 mm, which may include a Bragg grating written in one or both inner cores, that may be used for various optical devices, such as OADMs, optical filters, Mach-Zehnder interferometers, interleavers and wavelockers.
The telecommunications industry is currently striving to develop an all optical reconfigurable network. This reconfigurable network will require agile wavelength control devices such as tunable or xe2x80x9creconfigurablexe2x80x9d optical add/drop multiplexers (ROADMs), 2xc3x972 couplers, optical pumps and bandpass filters. A simple ROADM utilizes a 2xc3x972 coupler to combine distally located tunable Bragg gratings. This technology is undesireable because the insertion can exceed at least 3 dB. Alternatively, the 2xc3x972 couplers have been substituted with optical circulators. The combination of circulators and tunable gratings provide a simpler, lower loss and flexible features than the 2xc3x972 coupler embodiments. Unfortunately, the cost of the circulators makes this technology relatively expensive.
An alternate low loss OADM technology uses combinations of Mach-Zehnder interferometers (MZIs) and gratings structures. The fiber MZI/coupler technique requires precise control of the OPD, which is difficult to maintain with standard optical fiber interferometers in the face of the environmental perturbations typically experienced by telecom components.
Further, gratings written in the fuse region of couplers is also a viable low loss alternative to the circulator/grating configuration, but currently faces a variety of practical limitations, most of which are related to temperature stability and grating quality.
Other techniques are used to manufacture the 2xc3x972 couplers used in telecommunications components. For example, a pair of D-shaped fiber may be fused together and then stretched to taper the cores, and therefore reduce diameter of the cores and fused portion of the coupler. A grating is then written within the tapered region of the coupler. Some disadvantages of this technology is that the couplers are sensitive to the environment such at temperature variations and vibration. The reduced diameter tapered region also makes for flexible and fragile components, resulting in increase bending loss, stability and ruggedness. Further, tuning of the grating by straining the grating is difficult.
The 2xc3x972 couplers may also be formed using a dual core fiber. These fiber couplers exhibit similar disadvantages as the tapered couplers described hereinbefore.
It would be advantageous for provide a 2xc3x972 coupler, ROADM or similar optical component that provides environmental stability, tunablility and manufacturability.
An object of the present invention is to provide a coupler and/or optical add/drop multiplexer, including an optical waveguide with a reflective elements disposed therein, wherein optical waveguide has characteristic that provide a more rugged and tunable optical component.
In accordance with an embodiment of the present invention, an optical waveguide comprises an outer cladding and at least two cores disposed within the outer cladding. The cores are spaced apart a predetermined distance to couple light from a first core to the other core. The outer transverse dimension of the waveguide is greater than 0.3 mm.
In accordance with an embodiment of the present invention, an optical drop filter for dropping a wavelength band from an input optical signal is provided. The drop filter comprises an optical waveguide that includes an outer cladding and a pair of cores disposed within the outer cladding. The cores are spaced apart a predetermined distance to couple light from one core to the other core. An outer transverse dimension of the waveguide is greater than 0.3 mm. A grating is disposed in each core. Each grating has substantially the same reflection wavelength, wherein the reflection wavelength of each grating is substantially the same as the center wavelength of the wavelength band to be dropped.
In accordance with an embodiment of the present invention, an optical add/drop multiplexer for adding and/or dropping a wavelength band from an input optical signal is provided. The add/drop multiplexer comprises an optical waveguide that includes an outer cladding and a pair of cores disposed within the outer cladding. The cores are spaced apart a predetermined distance to couple light from one core to the other core. An outer transverse dimension of the waveguide is greater than 0.3 mm. A grating is disposed in each core. Each grating has substantially the same reflection wavelength, wherein the reflection wavelength of each grating is substantially the same as the center wavelength of the wavelength band to be dropped and/or added. The length of the waveguide is substantially equal to the coupling length.
In accordance with an embodiment of the present invention, an optical add filter for adding a wavelength band from an input optical signal is provided. The add filter comprises an optical waveguide that includes an outer cladding and a pair of cores disposed within the outer cladding. The cores are spaced apart a predetermined distance to couple light from one core to the other core. An outer transverse dimension of the waveguide is greater than 0.3 mm. A grating is disposed in each core. Each grating has substantially the same reflection wavelength, wherein the reflection wavelength of each grating is substantially the same as the center wavelength of the wavelength band to be added.
In accordance with an embodiment of the present invention, a bandpass filter for dropping a wavelength band from an input optical signal is provided. The bandpass filter comprises a first and second optical waveguide. Each of the first and second optical waveguides includes an outer cladding and a pair of cores disposed within the outer cladding. The cores are spaced apart a predetermined distance to couple light from one core to the other core. An outer transverse dimension of the waveguide is greater than 0.3 mm. A grating is disposed in each core. Each grating has substantially the same reflection wavelength, wherein the reflection wavelength of each grating is substantially the same as the center wavelength of the wavelength band to be dropped. The drop port of the first optical waveguide is optically coupled to the input port of the second optical waveguide.
In accordance with an embodiment of the present invention, an optical pump combiner for combining a first pump light centered at a first wavelength and a second different pump light centered at a second wavelength is provided. The pump combiner comprises an optical waveguide that includes an outer cladding and a pair of cores disposed within the outer cladding. The cores are spaced apart a predetermined distance to couple light from one core to the other core. The outer transverse dimension of the waveguide is greater than 0.3 mm. A grating is disposed in each core. Each grating has substantially the same reflection wavelength, wherein the reflection wavelength of each grating is substantially the same as the center wavelength of the wavelength band of one of the first and second pump lights. The length of the waveguide is substantially equal to the coupling length.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof.